An investigation into the tidal residual circulation in the Tasman/Golden Bays system was performed. This investigation involved collecting hydrographic and current meter data, and configuring a numerical circulation model. The model was able to reproduce the gross features of the major tidal flows within the system revealed by the data. The simulated tidal residual circulation conformed to that previously suggested, except along the western side of Tasman Bay where this investigation suggests that residual flows move northwards. The validated model was then used to produce simulations of the fate of the plumes from the major rivers. Salinity field simulations describing different river flow and wind direction/velocity scenarios suggest that the Motueka River plume can cover considerable proportions of western side Tasman Bay, extending into Golden Bay during flood conditions. The embedded sediment transport model was also used to investigate the fate of fine sediments entering the bays. Simulated distribution patterns of fine sediments entering the bays from the four major tributaries were found to be consistent with existing bathymetric and seabed substrate characteristics.